With the Business subscription, there are additional settings that allow you to choose who can contribute to Newsfeed pages. This allows you to share important information with your team without worrying about employees posting unrelated or unnecessary info.
When you create a new Page, you will see the option to choose who can post:
Everyone can post means anyone added as a member of the page will be able to add posts.
Only admins and managers can post means any users assigned to the admin or manager role can add messages.
Only specified users can post lets you choose certain users who can add messages. A field will appear where you can give users access.
For the 2nd and 3rd options, those who are added as members (users who can see the page and its posts) can still comment on posts.
Any of these options can be edited at a later time, so you have the option to add or remove restrictions as needed.
In your Settings > Company settings page, you'll also find a couple of options that allow you to restrict certain users' access to your Newsfeed:
Here you can disable the Newsfeed altogether if you need to, or prevent users designated as employees from creating their own newsfeed pages.